The invention relates to a semiactive night viewing system using light intensification. For normal passive viewing of a scene, the system comprises a large-aperture imaging-forming device which forms an image of the scene on an intensifier tube. The intensified image is transmitted to a television camera which is connected to a display apparatus via a control unit. By means of the control unit, the system can be switched to an active mode of operation in which a single flash of light, of a wavelength outside the visible spectrum, is emitted to produce a pulsed illumination of the central area of the scene.
Fully passive night viewing systems using light intensification are known, such as for example telescopes or binoculars using intensifier tubes (light weight equipment) or low-light-level television cameras (heavier equipment).
Further, active night viewing systems are known in which a light source illuminates the scene. Some of these systems use permanent illumination during the viewing period and others employ pulsed illumination which is synchronized which a shutter in the intensifier channel (tomofluoroscopy equipment).
Passive systems have the advantage that they cannot be detected, but their range is limited if the light level at night is low. Active systems have a very large range but they can easily be detected by the adversary.
U.S. Pat. No. 3,509,344 describes a device with a night viewing telescope. The device combines a passive system with an active system. The image of the scene which is illuminated by infrared radiation emitted by a light flash is converted into a visible image in the telescope by a converter tube.